The same point is that short-circuit protection can be realized. The principle of fuse is that the current flowing through the conductor will make the conductor heat. After reaching the melting point of the conductor, the conductor melts, so disconnect the circuit to protect the electrical appliances and lines from being burned out. It is an accumulation of heat, so overload protection can also be realized. Once the melt burns out, replace the melt.
The circuit breaker can also realize the short-circuit and overload protection of the line, but the principle is different. It realizes the open-circuit protection through the bottom magnetic effect of the current (electromagnetic release) and the overload protection through the thermal effect of the current (not fusing, and there is no need to replace the device). In practice, when the power load in the circuit is close to the load of the fuse used for a long time, the fuse will be heated gradually until it is fused. As mentioned above, the fusing of fuse is the result of the joint action of current and time, which plays a role in protecting the line. It is disposable. The circuit breaker is the protection for the instantaneous current increase of the circuit, such as when the leakage is large, or short circuit, or when the instantaneous current is large. When the cause is found out, it can be switched on and continue to be used. As mentioned above, the fusing of the fuse is the result of the joint action of current and time, while the circuit breaker will trip as soon as the current exceeds its set value, and the time effect can be almost ignored. Circuit breaker is a common component in low-voltage distribution. There are also some places suitable for fuses.
Performance comparison between fuse and circuit breaker:
- Main advantages and characteristics of fuse
1) Good selectivity. As long as the rated current of the fuse link of the upper and lower fuses meets the requirements that the overcurrent selection ratio specified in the national standard and IEC standard is 1.6:1, that is, the rated current of the upper fuse link is not less than 1.6 times the value of the lower fuse, it is considered that the upper and lower fuses can selectively cut off the fault current;
2) Good current limiting characteristics and high breaking capacity;
3) Relatively small size;
4) The price is cheaper.
- Main shortcomings and weaknesses of fuses
1) Replace the fuse link after fault fusing;
2) The protection function is single, with only one section of overcurrent inverse time limit characteristics. This protection is used for overload, short circuit and grounding fault;
3) In case of one phase fusing, the adverse consequences of two-phase operation will be caused to the three-phase motor. Of course, the fuse with alarm signal can be used to make up for it, and one phase fusing can disconnect the three phases;
4) Remote control cannot be realized. It is possible only when it is combined with electric knife switch and switch.
Non selective circuit breaker:
- Main advantages and features
1) After the fault is disconnected, it can be reset manually without replacing components, unless maintenance is required after cutting off large short-circuit current;
2) Long time delay release and instantaneous current release with inverse time limit characteristics are used as overload and short-circuit protection respectively, and each performs its own duties;
3) Remote control can be realized when operating the mechanism with electricity.
- Main shortcomings and weaknesses
1) It is difficult to realize selective cut-off between the upper and lower non selective circuit breakers. When the fault current is large, it is easy to cause the upper and lower circuit breakers to be disconnected instantaneously;
2) The relative price is slightly higher;
3) The breaking capacity of some circuit breakers is small. If the circuit breaker with small rated current is installed near the high-capacity transformer, the breaking capacity will be insufficient. The existing products with high breaking capacity can be met, but the price is high.
Selective circuit breaker:
- Main advantages and features
1) It has the above advantages of non selective circuit breaker;
2) It has a variety of protection functions, including long time delay, instantaneous, short time delay and ground fault (including zero sequence current and residual current protection). It can realize overload, open circuit delay, instantaneous action of large short-circuit current and ground fault protection respectively. The protection sensitivity is very high, and it is convenient to adjust various parameters, which can easily meet various protection requirements of distribution lines. In addition, it can have cascade protection function and better selective action performance;
3) Nowadays, most products have intelligent characteristics. In addition to the protection function, they also have electricity measurement, fault recording and communication excuses to realize the centralized monitoring and management of power distribution devices and systems.
- Main problems
1) The price is very high, so it should only be used at the head end of distribution lines and sub trunk lines in particularly important places;
2) Larger size.